1. Field of the Invention
This invention relates to apparatus for treating lengthwise traveling material, particularly such apparatus for creping, microcreping or compacting a flexible web material, such as paper, textile, metal foil or plastic.
2. Description of the Prior Art
In one type of creping apparatus of the prior art, the material is adhered to a traveling driving surface such as that of a rotating drum or roll, and is creped by scraping it off that surface with a doctor blade. The traveling surface may be smooth, in which case a straight edged doctor blade produces a transverse crepe in the material, or the surface may be corrugated, that is, provided with alternating grooves and lands parallel to the direction of travel. In the latter case, means are provided for forcing the material into the grooves and the doctor is provided with teeth engaging in the grooves and intervening slots engaging the lands so that a longitudinal creping of the material is produced, as in U.S. Pat. Nos. 1,447,699 and 1,582,839.
In a different type of creping apparatus of the prior art, the material is not adhered to the traveling surface which is smooth, transverse creping of the material being effected by a combination of retarding and compressive forces exerted on the material during its travel on, and removal from, the driving surface. In this type of apparatus, a doctor blade is also commonly use, not to scrape the material from the driving surface but rather to form a retarding surface against which the traveling material impinges and which deflects the material away from the driving surface, as in U.S. Pat. No. 3,260,778.
This invention relates to apparatus of the second above-mentioned type, as exemplified by aforesaid U.S. Pat. No. 3,260,788 . In such apparatus, although the retarding member does not function as a scraper, it has been found necessary to force the retarder edge into engagement with the driving surface in order to prevent the material from snagging on or "driving" under the edge of the retarding member, with resultant loss of material and processing time. This not only causes undesirable wearing away of the retarding member, but also, due to irregularities and roughness produced by wear, causes snagging and diving of the material to occur. This problem has been so acute as to prevent satisfactory use of such apparatus for processing certain types of materials, such as thin, light webs or those with surface roughness, particularly prone to snagging or diving.